The present invention relates to a line head module used as an exposing unit in an image forming apparatus and to an image forming apparatus having the line head module.
A line printer (image forming apparatus) has been known as a printer using an electrophotographic system. In the line printer, a charging unit, a line-shaped printer head (line head), a developing unit, a transfer unit, etc. are adjacently arranged on a peripheral surface of a photoconductor drum to be exposed. That is, an electrostatic latent image is formed on the peripheral surface of the photoconductor drum charged by the charging unit, as a light-emitting element disposed in the printer head exposes by selectively performing light-emitting operations. Then, the electrostatic latent image is developed by toner supplied from the developing unit, and the developed toner image is transferred to a paper sheet by the transferring unit.
Recently, a light-emitting diode has been generally used as the aforementioned light-emitting element of the printer head. However, there has been a problem that it is difficult to ensure light-emission intensity and responsiveness. Therefore, recently, an image forming apparatus having a light-emitting element array, which uses an electro luminescence element (organic EL element) as a light-emitting element, as an exposing unit has been proposed (for example, see Japanese Unexamined Patent Application Publication No. 11-198433).
The image forming apparatus has adopted an exposing system in which radiant light from the printer head (line head) forms an image on the photoconductor drum through a SELFOC (registered trade mark) lens array manufactured by Nippon Sheet Glass Co., Ltd. The lens array has a plurality of lens elements, which form an image as a nonmagnified erect image, in order to make it possible to form a wide range of image by superposing.
The aforementioned organic EL element has problems that durability is deteriorated due to moisture absorption, which further leads to a short lifetime. However, a measure against the moisture absorption of the organic EL element has not been disclosed at all in the Japanese Unexamined Patent Application Publication No. 11-198433.